My PSU is 530W but its not saying anything like SLI READY because its not a Cooler Master PSU, it just a china PSU i bought at $20 (530W)

I reall need an idea before im goin to buy a new PSU, should I buy ? I love SLI, and if i buy, how much W is needed ? Cooler Master 450W or 500W or 550W ?

Thanks